Emerging wireless network technologies may include wireless networks designed with a packet-switched architecture. Such a network may be referred to herein as a wireless packet-switched network (WPSN). A mobile wireless device (“mobile node”) operating within a WPSN may be capable of communicating a variety of media, including perhaps data, voice, and video, among others. Internet protocol (IP) datagrams may be utilized.
A mobile node that is connected to a WPSN may alternate between states of active transmission and reception or inactivity. Intervals associated with these states may depend upon characteristics of an application supported by the connection. An Institute of Electrical and Electronic Engineers 802.16e™ standard may specify special modes of operation designed to conserve battery power and air link resources during periods of inactivity. Additional information regarding the IEEE 802.16e™ protocol standard may be found in 802.16e™: IEEE Standard for Local and Metropolitan Area Networks—Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems—Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands (published Feb. 28, 2006).
The mobile node may negotiate the periods of inactivity with a serving base station. These periods may be known as sleep intervals. Sleep intervals may alternate with listening intervals. “Keep-alive” packets may be exchanged during listening intervals in order to maintain the network connection. Durations of sleep intervals and listening intervals may be a function of power saving class attributes associated with active connections maintained by the mobile node. Power saving classes may take into consideration quality-of-service (QoS) parameters associated with active connections. These dependencies may operate to control sleep intervals and listening intervals such that latency requirements associated with the various connections may be satisfied.
The mobile node does not communicate with the serving base station during sleep intervals. Thus, the mobile node may power down one or more operational components or may perform other activities that do not require communication with the serving base station during sleep intervals. During listening intervals, however, the mobile node is expected to receive all downlink transmissions as in normal operation.
To prevent packet loss, the serving base station may buffer traffic addressed to connections bound to the sleeping mobile node. The serving base station may subsequently broadcast a traffic indicator message to the mobile node during the next listening interval to alert the mobile node that packets await transmission in the downlink. The traffic indicator message may be broadcast from the serving base station to all associated mobile nodes that are in sleep mode and that have downlink traffic pending.
During a listening interval, the mobile node may return to normal (non sleep-mode) operation if it decodes its own connection identifier from the traffic indicator message. A lack of synchronization with the serving base station may also force the mobile node to return to normal-mode operation. In the absence of any such normal-mode triggers, the mobile node may begin a new sleep interval.
The serving base station may maintain a service context for the mobile node during sleep-mode operation. The service context may comprise parameters indicative of types of applications and of a QoS level associated with the current connection. The mobile node may remain within a range of the serving base station between a time of initiating the sleep-mode cycle and a start of the next listening interval. In that case, any downlink packets buffered in the serving base station can be forwarded to the mobile node after the mobile node transitions to the listening mode, receives the traffic indicator message, and resumes normal operation.
Some mobile nodes may be capable of a macro-diversity mode of operation. One or more active power-saving classes may require maintenance of a serving base station identifier (BSID). The power-saving classes may also require maintenance of a list of potential serving base station candidates (a “diversity set”), perhaps ordered according to some priority. If a macro-diversity hand-off (MDHO)/fast base station switching (FBSS) duration as specified in a mobile sleep response message has not expired, the macro diversity-capable mobile node may continue to update the diversity set and the serving BSID while in sleep mode. Downlink traffic may be buffered for the mobile node at each base station in the diversity set during the sleep-mode interval. The buffered traffic may be forwarded to the mobile node by the serving base station during the next listening interval.
Other mobile nodes may be incapable of macro diversity-mode operation, however. Any downlink packets buffered for a non macro diversity-capable mobile node in the prior-serving base station before handoff may be lost.